(a claimant of the alternative fuel credit that is also a Form 720 filer for any I.R.C. Sec. 4041 tax must first offset that liability on Form 720 and may claim any remaining balance of the credit on either Form 8849 or Form 4136; if claimant is not a Form 720 filer for any I.R.C. Sec. 4041 tax, claimant can claim entire amount on Form 4136; claim can be made for any open year for which credit available after claimant obtains registration number).